Alternating-current generator



(No Model.) 2 sheets sheet 1.

- 7 0. s. BRADLEY;

ALTERNATING CURRENT GENERATOR.

Patented 001:. 5,189?

mva'moa A ATTORNEY WITNESSES: I 6.Kwm

(No Model.) 2 Sheets-Sheet '2.

G.S.BRADLEY. ALTERNATING GURRENT GENERATOR. $10,591,267. Patentad 0 t.5,'1897 WET 391W iTPHT o A; ATTORNEY UNITEn STATES PATENT OFFICE;

CHARLES s. BRADLEY, OF Avomnn'w ronmnssrenon TO THE GENERAL EL oTRIo COMPANY, OF NEW YORK.

'ALTERNATlNG-GU BRENT GENERATOR.

@EEOIFICRTIQN fog part of Letters Patent No. 591,267, dated October 5, 1897.

Application filed June 22,1896. Serial lilo. 596,425. (No model.)

Fa ale? whom it may concern/.-

Be it known that I, CrrAR'LEs S. BRADLEY, a citizen of the United States, and a resident of Avon, in the county of Livingston, in the State of New York, have invented certain new and useful Improvements in Alternating Current Generators, of which the following is a specification.

This invention relates to dynamo-electric io generators, the object being to generate a current or currents of variable frequency or rate of alternation with a prime mover operating at practically constant speed.

The invention is especially designed for service in connection with induction-motors which when provided with secondary wind ings of constant resistance require a low firequency and electromotive forcein starting and an increased frequency and electromoac tive force-as the speed rises.

In carrying out my invention I develop a rotary magnetic field by currents furnished I by an exciter in one element of the generator and drive said exciter by the prime mover at a variable speed, thus producing any desired speed of the magnetic poles with relation to the cooperating element of the generator, the winding of which connects with a distribution-circuit containing the in- 0 duction-motors. The connections with the exciter are so arranged that the direction of polar travel of the rotary field is opposite to the bodily movement of the core in which said rotary field is set up, thus establishing 5 a differential speed of polar travel with relation to the generating winding. The circuit including the'magnetizing generator-winding is provided with adjusting devices-for varying its capacity or inductance, or both, to ren- 0 der the circuit resonant to the different rates of alternation which may be set up by the exci-ter. The result is preferably eftected by adjustable condensers controlled by the same device which regulates the speed oi the ex- 5 citer, so that resonance or approximateresonance may be maintained in the excitercircuits throughout its working range of speed.

The invention is especially applicable to so plants in which a number of motors aresimultaneously varied in speedas, for example,

in operating cars or trains of cars. In such cases the organization I provide forms a selfcontained equipment of the type, for example, described in a prior patent granted to me, No. 399,372, dated March 12, 1889.

The invention comprisesin its broadest aspect a variable-rate generator operated by a prime mover of constant or approximately constant speed.

It comprises also a method of varying the rate of an alternating-current generator by developing a rotary field of variable speed, and also in rendering the circuits resonant to the several speed adjustments. o 5

It comprises also; means for developing a variable -speed rotary field in a generator and rendering the circuits resonant to the several speed adjustments.

It comprises also more specific features, which will be hereinafter fully described,and will be definitely indicated in the claims.

In the accompanying drawings, which diagrammatically illustrate my invention, Figure 1 is a diagram of the invention, the speed- 7 5 varying devices of the exciter being omitted for clearness ofillustration. Fig. 2 is a diagram of the speed-varying devices for the exciter, and Fig. 3 illustrates a modified form of generator-Winding. 8o

1 2 3 represent a series of induction-motors, in the primary element of which is set up a rotary magnetic field by polyphase currents in the mains a b o. The motor-secondaries are provided with closed circuits,which may be of constant resistance. These are shown at 1 2 3 as simple squirrel-cage windings.

The mains may be charged with polyphase currents of any order, as triphase, quarterphase, duo. Fig. lshowsthesystem organized for triphase currents and Fig. 3 for quarterphase currents.

on b c are mains connecting with three symmetrical'points of the generating-winding of a generator 4. The magnetizing-winding 5 of this generator is driven by a prime mover acting, for example, on a pulley 6. (See Fig. 2.)

7 is an exciter which is geared or otherwise connected with the shaft which carries the too winding 5 by a variable-speed device (shown as two cone-pulleys 8 8) with an intervening coupler or belt 9 and a shipper 10.

The windings of the generator and exciter are shown diagrammatically, similar reference-figures being used to show corresponding parts. The field-magnet of the exciter may be charged bya direct current or inany suitable way. Its armature is tapped at a plurality of symmetrical points leading through ring-contacts 11 11 11 upon which bear brushes leading to the magnetizing-winding of the generator through corresponding brushes and ringcontacts .12 12 12*. B61 tween the eXciter-armature and the generator. are devices 13 13 13* for varying the capacity inductance product of the circuits.

By a proper adjustment the circuits-maybe rendered resonant. to anyrate OftlilGllHfi-z tion, and when so adjusted the opposing'efe' feet of inductance is eliminated and electromotive force and resistance are the only-factors affecting the strength-of current and a large current will flow in the circuits, per mitting an exciter of small size to be employed to set up the rotary field of the generator.

Resonance may be established-byiadjustw ing either the capacity or the-inductance of the circuits, theproduct of thecapacityinmicrofarads and the inductance in henriesvarying inversely as the square-of thenumber of alternations per second in the magnet. izing-winding.- I .preferto use-acondenser or condensers as theadjusting.elemenia and one such is shown for each branch-ofthe fart= phase circuit at 13 13"13", being arranged-so that moreor less surfaceimaybe cutin by; the same operation of the handle 14: which throws the shipper andspeedi-regulatorn Thev parts are-soarranged that the capacitywi-ll. be least when the motorsane beingstarted-f since the rate .supplied to the .motoninstara' in g should. be .slow-,. which requiresthe speed;

of the rotary field to beclosen-t'o that 0f the revolving core-that isto. say, the rotanyfield, andv therefore the eXcit'er,'- should.have

a maximum speed and maximumirate which will be in tune with the circuitiwhentheda't ter has the-leastcapacity. As-theomotors rise in speed, the capacity is'increasedby a movement of the controlling-handle andithe rate of the exciter is slowed down bytheac companying movement of the shipper.

The brushes v12 12 12 are connected with the eXciter-leads insuchorde'r: as to develop a rotary magnetiefield on=thetmagnetizingwinding of .the generator -.in an opposite tdivrection to the .motion imparted to thecore by the shaft. Thus the actual speed of travel of the rotary-field poles relatively to the gencrating-winding is ditferentialand-may be. of any value from zero to the maximum dificr-i enceof speed: Thusit will 'be -seen thatin starting up the handle may be thrownto the. left, giving-a high speed to the cxciter-armae. ture and a low speed of cutting ofthe generating-Wi-nding by-the lines of therotary-field by reason of the close approximation in speed of the poles and the core and in opposite directions. The motors thenstart with their primaries excited by currents of low rate and low electromotive force. The handle is then gradually shifted to the right, producing an increased rate and electromotive force in the circuits (1-?) c and driving the induction-motors at increased speed.

It will of course be understood that it is relalive motion of the two elements of the generator which controls the generation of current and that either may be the rotating element, anilithat the anrangement of the two elements as to outside and inside parts is also reversible. it is not necessary that the exciter should doliver polyphase currents to the magnetizingcircuit, as single-phase currents will set up a rotary magnetic-field under the reaction of the cooperating element of the generator, cs-

peeially when induction-motors are connected with the distribution circuit. Such an arrangement is shown in Fig. 3 of the drawings;

I claim as new' and desi-re tdsecureby, Lets.

ters -Patent,-' is- 13 An alternatingcurrent electric gener- They may ator-provided-with means forvary-ing the rate of -alternation;-andadjusting-devices to very the -"product oli'capaeity: and inductance to produce resonance at the severalrates. 1 2. An alternating-current generator -provided-with'a rotary-field winding on'its -magnetizing element; an--alternating-current excitenfor f urnishing-the magnetizing-current, andmeans for varying'th'e rate ofthe exciter.

vide d With-a rotary-field windingonits maghetizing' element, a-polyphase exciter,- and means'forwary-ing-the rate ofthe exciter.

4. Anzalternating current generator provided witha rotary field winding omits ma netizing-eleunena-an exeiter of variable rate;

andadjnsting devices for varying the product ofcapaeityandinductance to produce electrioalresonanoe.

5.- The methodrofvarying the rate of an-ah ternat-ingcurrcntconsisting in causing a dif- 3. An-alternatingwurrent generator proferentiahmotion of the magnetic poles set up bya chargin g eurrent-and thecore magnetized by said charging-current-relatively to the generating-winding andivarying said differential motionr 6." The methodof varying the rate of anal ternating-cum'ent generator,- consisting in developing a rotary magnetic field in one wind-- ing and var ying the rate ofuotation of the field.

veloping arotary magnetic field in its magnetizing-winding, and varying the rate of retation of the field, and simu1taneous1yadjnst-. in g the circuits for electrical resonance at the different rates.

8. An alternating-current generator com-' prising a rotary field winding driven by a prime mover, an exciter for charging the field,

- and means for varying the speed of timesciter.

9. An alternating-current generator comprising a rotary-field winding driven by a prime mover, an exciter for charging the field,

means for varying the speed of the exciter,

and adjusting devices for varying the capacity inductance product of the field-circuits to produce electrical resonance.-

' 10. The combination of an induction-motor, a generator having its generating-winding connected therewith, and a rotarydieid winding on its magnetizing element, and means for varying the speed of the rotary field.

11. The combination of an-induction-motor, an induction-generator having its secondary connected with said motor and a rotary-field winding on its primary, means for CHARLES S. BRADLEY.

Witnesses:

Guns. EDGAR MILLS, Boer. II. READ. 

